JP3399517B2 - Gas laser device that emits ultraviolet light - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas laser device which emits ultraviolet rays, and more particularly to a gas laser device which emits ultraviolet rays such as an excimer laser device having high oscillation efficiency.

[0002]

2. Description of the Related Art As semiconductor integrated circuits become finer and more highly integrated, projection exposure apparatuses are required to have improved resolution. Therefore, the wavelength of exposure light emitted from the exposure light source is being shortened, and a gas laser device that emits ultraviolet rays such as an ArF excimer laser device and a fluorine laser device is effective as a next-generation semiconductor exposure light source. .

In the ArF excimer laser device, a mixed gas of fluorine (F ₂ ) gas, argon (Ar) gas and a rare gas such as neon (Ne) as a buffer gas, and in the fluorine laser device, fluorine ( F
₂ ) Helium (He) as gas and buffer gas
Laser gas, which is a mixed gas consisting of rare gases such as
A pair of main discharge electrodes, which are enclosed in a laser chamber at 0 kPa and are opposed to each other with a predetermined gap, are provided inside the laser chamber. A laser gas, which is a laser medium, is excited by generating a discharge at the main discharge electrode inside the laser chamber.

In order to efficiently generate a laser beam, it is necessary to generate a uniform discharge between the main discharge electrodes, but in order to generate a uniform discharge in a high pressure gas atmosphere of several 100 kPa, Usually, it is general to pre-ionize the laser gas existing in the discharge space between the main discharge electrodes before starting the main discharge.

As one of the means for generating the above-mentioned preionization, there is a preionization method in which two electrodes are arranged so as to face each other with a dielectric material interposed therebetween. Examples of the preionization unit are disclosed in JP-A-5-327070 and JP-A-2,794.
792, JP-A-10-242553, and JP-A-8-5
No. 02145 and the like. The preionization section described in any of the above is a first electrode (hereinafter, referred to as an outer electrode) that comes into contact with the outer surface of the cylindrical body formed of a dielectric material, and a second electrode inserted inside the cylindrical body. And an electrode (hereinafter, referred to as an inner electrode). By generating a potential difference between the outer electrode and the inner electrode, corona discharge is generated between the outer electrode and the dielectric cylinder. Is generated, and the laser gas existing in the discharge space between the main discharge electrodes is preionized by the ultraviolet light generated at this time. In addition, in the above-mentioned preliminary ionization means, the dielectric cylinder and the outer electrode may not be in contact with each other and may be in close proximity to each other, or the outer electrode may be covered with the dielectric substance.

[0006] The ultraviolet rays adopting the above-mentioned preionization system
Emitting gas laser device (hereinafter simply referred to as gas laser device
To do. 5) shows an example of the configuration of the excitation circuit of FIG. This excitation times
In the road, use solid state switch SW such as IGBT
Moreover, it has a circuit configuration called a capacitance transfer type circuit.
The operation will be briefly described according to this circuit diagram.
When the SW is open, the charge from the high voltage power supply HV
Is the capacitor C₁Stored in. Capacitor C₁To charge
When the switch SW is closed while the
C₁Is the capacitor C₂Move to. Capacitor C
₂Charge transferred to the magnetic switch or supersaturation
Non-linear inductance L called dactance_mThrough
Peaking capacitor C₃Move to. At this time,
Itch L _mThe pulse width of the applied voltage is compressed by the action of
It The magnetic switch L_mThe action of the capacitor C₁
Is the capacitor C₂Inductance during transition to
Is large and the magnetic flux density is large and saturated, the inductor
The capacitance decreases sharply and the capacitor C can be used efficiently.₂
Peaking capacitor C₃Move to. Pee
King capacitor C₃Voltage increases, and the discharge breakdown voltage
Reach the main chamber, the main
A pulse discharge is generated between the electric electrodes 3 and 4, and the laser gas is excited.
The start is done. That is, the thick line in FIG.
A current flows through the discharge circuit loop indicated by.

A capacitor C ₁₁ is provided in parallel with the main discharge electrodes 3 and 4.
A voltage divider circuit composed of C ₁₂ and C ₁₂ and an inductance L ₀ is connected, and the pulse voltage applied between the main discharge electrodes 3 and 4 is divided by 25% as shown in FIG. 6 described later.
Between 75% and 75%, and between the inner electrode 7 and the outer electrode 9 of the corona preionization part 15 arranged close to the upstream side and the downstream side of the main discharge space between the main discharge electrodes 3 and 4. A voltage for corona discharge is applied. The voltage division ratio in the voltage dividing circuit, the capacitances of the capacitors C ₁₁ and C ₁₂ , and the value of the inductance L ₀ are optimally selected to set the time constant to a desired value, and the timing of corona preliminary discharge with respect to the main discharge is adjusted. The combined capacitance of this voltage dividing circuit is adjusted to 10% or less of the peaking capacitor C ₃ .

By the way, it is generally known that the lower the inductance formed by the discharge circuit loop, the higher the laser oscillation efficiency (Medao Maeda, "Excimer Laser," pages 64-65, Academic Society of Japan). Publishing Center 19
August 20, 1983 first edition).

[0009]

FIG. 6 shows an actual configuration example of the above-mentioned discharge circuit loop. FIG. 6 is a cross-sectional view of a main part of the gaz laser device perpendicular to the laser oscillation direction.
The constituent elements denoted by the same reference numerals as in FIG. 5 correspond to the constituent elements shown in FIG.

Briefly, an insulating base 21 is airtightly fitted in the upper wall of the laser chamber 1 along the length of the discharge space, and the other main electrode (for example, cathode) 3 is attached to the center inside the laser chamber 1. The high voltage power source 1 is pierced through the insulating base 21 by the current introducing member 23.
It is connected to 0. Here, the high-voltage power supply 10 corresponds to the circuit portion including the nonlinear inductance L _m on the left side of the peaking capacitor C _{3 in} FIG. Laser chamber 1
Inside, a pair of current-carrying members 25 are attached to the insulating base 21 substantially in parallel along both sides of the main electrode 3,
A conductive base 26 is stretched between the tips of the current-carrying members 25, and one main electrode 4 (for example, an anode) is attached at a position facing the main electrode 3 at the center of the conductive base 26. Outside the laser chamber 1, a peaking capacitor C ₃ composed of a large number of capacitors connected in parallel on both sides of the current introducing member 23 is connected, and the peaking capacitor C ₃ includes a current introducing member 24 penetrating the insulating base 21. It is connected to the current-carrying member 25 via. Further, the dielectric cylinder 8 is provided at a position on the upstream side and the downstream side of the laser gas flow 2 indicated by the arrow above the conductive base 26 and in which the main discharge space between the main electrodes 3 and 4 is expected. A preionization section 15 in which the outer electrode 9 and the inner electrode 7 are arranged opposite to each other is arranged, the outer electrode 9 is directly connected to the conductive base 26, and the inner electrode 7 is connected to a high voltage power source 1 via a terminal (not shown).
It is connected between zero capacitors C ₁₁ and C ₁₂ .

In the configuration of FIG. 6, the portion surrounded by the alternate long and short dash line is the discharge circuit loop described with reference to FIG. 5, and the current introducing member 23 penetrating the insulating base 21 and the main portion connected to the current introducing member 23. The electrode 3, the main electrode 4, the conductive base 26 on which the main electrode 4 is installed, the conductive member 25 connected to the conductive base 26, the current introducing member 2 connected to the conductive member 25 and penetrating the insulating base 21.
4. The peaking capacitor C _{3 is} formed by connecting the current introducing member 24 and the current introducing member 23.

As described above, the lower the inductance formed by the discharge circuit loop, the higher the laser oscillation efficiency. Since this inductance is proportional to the cross-sectional area of the discharge circuit loop (area of the cross-section in FIG. 6), it is necessary to make the cross-sectional area as small as possible. That is, the current introducing member 23, the main electrode 3, surrounded by the one-dot chain line in FIG.
The cross-sectional area of the space surrounded by the main electrode 4, the conductive base 26, the energizing member 25, the current introducing member 24, and the peaking capacitor C ₃ needs to be small.

However, the potential difference between the current introducing member 23, the main electrode 3, the peaking capacitor C ₃ and the laser chamber 1 which is normally grounded is as large as about 20 to 30 kV, and if these distances are too close, dielectric breakdown occurs. Occurs.
Therefore, the size of the insulating base 21 cannot be made too small.

The distance between the main electrodes 3 and 4 defines the size of the emitted laser light, but the size of the laser light is limited to some extent according to the application. For example, Ar for semiconductor exposure is used.
In the case of the F excimer laser, it is 15-18 mm, so
It can't be too short.

The size of the conductive base 26 cannot be made too small because the preionization parts 15 are arranged on both sides of the main electrode 4.

Further, the conductive base 26 and the current introducing member 2
The cross-sectional area of the discharge circuit loop can be reduced by bringing the position of the current-carrying member 25 connecting 4 to the preionization unit 15 side. However, since the current-carrying member 25 has the same potential as the outer electrode 9 forming the preliminary ionization part 15, if the current-carrying member 25 is brought too close to the preliminary ionization part 15, the current-carrying member 25 acts similarly to the outer electrode 9. Become. Then, corona discharge also occurs on the side opposite to the discharge space between the main electrodes 3 and 4, and the ultraviolet rays generated by this corona discharge do not reach the discharge space, and do not contribute to the preliminary ionization of the laser gas existing in the discharge space. That is, the energy supplied to the corona discharge generated between the outer electrode 9 and the dielectric cylinder 8 is reduced by the above-mentioned extra corona discharge, and pre-ionization may be insufficient.

Also in the UV arc preionization system, Applied Physics B, Vol. 63, 1-
As described in page 7, JP-A-3-283785, etc., when the current-carrying member is located outside the pair of electrodes for preionization (on the side opposite to the electrodes) and is too close to the preionization electrodes. Since the discharge breakdown occurs between the preionization electrode and the high voltage side, it cannot be made too close to each other, so that the cross-sectional area of the discharge circuit loop cannot be reduced.

In the case of the excimer laser device manufactured by the present inventors in the past, the inductance formed by the discharge circuit loop in FIG. 6 was 10 nH at the minimum.

The present invention has been made to solve the above problems of the prior art, and an object thereof is to reduce the cross-sectional area of the discharge circuit loop in the excitation circuit of a gas laser device that emits ultraviolet rays. To reduce the inductance and improve characteristics such as laser oscillation efficiency.

[0020]

A gas laser device for emitting ultraviolet rays according to the present invention which achieves the above object, has a laser chamber filled with a laser gas and having a circulation means for circulating the laser gas therein, and a laser chamber inside the laser chamber. A discharge circuit including a pair of main discharge electrodes arranged at a predetermined interval and a peaking capacitor connected in parallel to the pair of main discharge electrodes, and a first electrode and a second electrode facing each other via a dielectric. A gas laser device for emitting ultraviolet rays, wherein the pre-ionization means is disposed, and the pre-ionization means is disposed adjacent to both sides of the one main discharge electrode along the one main discharge electrode. Is a main discharge electrode on the ground side, and the one main discharge electrode and the peaking capacitor pass between the one main discharge electrode and the preionization means. The preionization means are connected by an electric member, and the preionization means includes a second electrode covered with a dielectric substance and a first electrode contacting the dielectric substance around the second electrode. Is applied with a high voltage, and the conducting member and the first electrode are integrated with each other.

In this case, the current-carrying member is composed of a conductive plate having an opening, through which the laser gas passing through the main discharge space between the main discharge electrodes passes and the ultraviolet rays from the preionization means are passed. It is desirable that they are arranged so as to reach the main discharge space.

[0022]

In the present invention, the one main discharge electrode and the peaking capacitor are connected by the current-carrying member passing between the one main discharge electrode and the preionization means.
Since the cross-sectional area of the discharge circuit loop in the excitation circuit is reduced and the inductance of the discharge circuit loop can be further reduced, the characteristics such as laser oscillation efficiency of the gas laser device that emits ultraviolet rays can be improved. The preionization means is composed of a second electrode covered with a dielectric substance and a first electrode that abuts the dielectric substance around the second electrode, and the above-mentioned current-carrying member and its first electrode are Since they are integrated, the preliminary ionization portion can be brought close to the main discharge space, the intensity of the ultraviolet rays reaching the main discharge space is increased, and the preliminary ionization is strengthened, so that the laser characteristics can be improved.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the gas laser device of the present invention will be described below.

FIG. 1 is a sectional view of a main part of a gas laser device according to a first embodiment of the present invention, which is perpendicular to the laser oscillation direction.
FIG. 2 is a side view thereof. In this embodiment, the excitation circuit has a structure as shown in FIG. 1 and 2, a fan for circulating the laser gas enclosed in the laser chamber 1 therein, a heat exchanger for cooling the laser gas, and the like are omitted from the drawing. Further, in the side view of FIG. 2, the preliminary ionization section 15 is not shown.

This gas laser device includes a laser chamber 1
On the upper wall of the insulating base 21 along the length of the discharge space.
Is hermetically fitted, the other main electrode (for example, cathode) 3 is attached to the center inside the laser chamber 1, penetrates the insulating base 21, and is connected to the high-voltage power supply 10 by the current introducing member 23. Here, the high-voltage power supply 10 corresponds to the circuit portion including the nonlinear inductance L _m on the left side of the peaking capacitor C _{3 in} FIG.

In the laser chamber 1, a pair of current-carrying members 25 are attached to the insulating base 21 along both sides of the main electrode 3 so as to approach each other as they move toward the tips, and between the tips of the current-carrying members 25 and both sides thereof. The conductive base 26 is stretched over so as to spread over the conductive base 26, and one main electrode 4 (for example, an anode) is mounted on the conductive base 26 at a position facing the main electrode 3 between the tips of the pair of current-carrying members 25. Has been.

Further, the main discharge space between the main electrodes 3 and 4 is an upper region outside both of the positions where the tips of the pair of conductive members 25 of the conductive base 26 are connected, and through the respective conductive members 25. Dielectric cylinder 8
A preionization section 15 in which the outer electrode 9 and the inner electrode 7 are opposed to each other is arranged via the outer electrode 9, the outer electrode 9 is directly connected to the conductive base 26, and the inner electrode 7 is a terminal (not shown). Through the capacitors C ₁₁ and C _{12 of} the high-voltage power supply 10.
Connected between.

Outside the laser chamber 1, a peaking capacitor C ₃ composed of a large number of capacitors connected in parallel on both sides of the current introducing member 23 is connected, and the peaking capacitor C ₃ penetrates the insulating base 21 to introduce the current. It is connected to the current-carrying member 25 via the member 24.

As is apparent from the side view of FIG. 2, the current-carrying member 25 is formed of a conductive plate which is hollowed out to form an opening 27 except for the thin current-carrying portions extending vertically at a predetermined interval. The laser gas flow 2 is allowed to flow through the part 27 into the main discharge space between the main electrodes 3 and 4 without interruption, and the ultraviolet rays 16 generated by the corona discharge in the preionization part 15 pass through the opening 27. So as to reach the main discharge space between the main electrodes 3 and 4.

In the configuration of FIG. 1, the portion surrounded by the alternate long and short dash line constitutes the discharge circuit loop described with reference to FIG. 5, and the current introducing member 2 penetrating the insulating base 21.
3, a main electrode 3 connected to the current introducing member 23, a main electrode 4, a conductive base 26 on which the main electrode 4 is installed, a conductive member 25 connected to the conductive base 26, a conductive member 25 connected The current introducing member 24 penetrates the insulating base 21, and the peaking capacitor C ₃ is connected to the current introducing member 24 and the current introducing member 23.

The difference between this embodiment and the prior art shown in FIG. 6 lies in the arrangement of the conducting member 25 whose ends are connected to the conductive base 26 and the current introducing member 24 penetrating the insulating base 21. . In the prior art of FIG. 6, the energizing member 25
While the connection point between the conductive base 21 and the conductive base 21 is arranged outside the preionization part 15 (on the side opposite to the main electrode 4), in the present embodiment, the connection between the conductive member 25 and the conductive base 21 is performed. The dots are arranged so as to be located between the main electrode 4 and the preliminary ionization section 15.

As described above, the conductive member 25 is arranged to pass between the one main electrode 4 and the preionization section 15, and the preionization section 15 is arranged on both sides of the main electrode 4 so that the conductive base is formed. Although the size of 21 cannot be made too small, from the main electrode 4 in the discharge circuit loop,
The path leading to the current introducing member 24 via the conductive base 26 and the current-carrying member 25 can be shortened, and the cross-sectional area of the discharge circuit loop can be made smaller.

As described above, in order that the ultraviolet rays 16 for preionization generated in the preionization section 15 reach the main discharge space, the energizing member 25 has the opening 2 as shown in FIG.
7 is provided.

Generally, in a gas laser device, after the main discharge is generated between the main electrodes 3 and 4, the temperature distribution of the laser gas existing in the main discharge space becomes non-uniform,
If this is left as it is, the next main discharge will be non-uniform and efficient laser oscillation cannot be achieved. Therefore, before the next main discharge occurs, the laser gas is circulated by a fan (not shown) in the laser chamber 1 in order to replace the laser gas located in the main discharge space. The laser gas flow is indicated by reference numeral 2 in FIG. The opening 27 of the current-carrying member 25 also has an effect of not preventing the circulating laser gas flow 2 flowing in the main discharge space from reaching the main discharge space. The opening ratio of one metal plate of the opening 27 is 90%
The above is effective.

Even if the current-carrying member 25 is constructed by arranging a plurality of thin flat plates at predetermined intervals so as to secure the openings 27 through which the laser gas flow 2 and the ultraviolet rays 16 pass, the openings may be formed on a single metal plate. Although it may be configured such that 27 is removed,
The latter is more advantageous in the following points.

In the structure shown in FIGS. 1 and 2, the current-carrying member 25 is
It is arranged between the main electrode 4 and the preionization unit 15. When a plurality of thin flat plates are arranged at predetermined intervals to secure the opening 27, the thickness of the plurality of thin flat plates needs to have a certain thickness in order to secure its own strength. At that time, if the thickness is increased in the direction perpendicular to the direction of the laser gas flow 2, the laser gas flow 2
Therefore, the thickness is increased in the direction parallel to the direction of the laser gas flow 2. Then, the preliminary ionization part 15 is moved away from the main discharge space by this thickness, so that the ultraviolet rays 16 that reach the main discharge space as the thickness of the discharge member increases.
Of the laser beam is reduced by that amount, the preionization is weakened, and the laser characteristics are deteriorated.

On the other hand, in the case of the latter, since it has an integrated structure in which the opening 27 is cut out in one metal plate, even if the thickness in the direction parallel to the direction of the laser gas flow 2 is thinner than that of the former. , The strength can be secured. Therefore, as compared with the former case, the preliminary ionization section 15 can be brought closer to the main discharge space, the intensity of the ultraviolet rays 16 reaching the main discharge space is increased, the preliminary ionization is increased, and the laser characteristics can be improved.

FIG. 3 shows a cross-sectional view of a main part of a gas laser device of a second embodiment of the present invention which is a modification of the above embodiment, and is a side view thereof. The difference between this embodiment and the first embodiment is that the current-carrying member 25 shown in FIGS.
And the outer electrode 9 of the preionization unit 15 is integrated.
Others are the same as those in the first embodiment.

In the case of this embodiment, on the side surface of the current-carrying member 25,
A linear metal member forming the outer electrode 9 is integrated by welding or the like at a position close to the dielectric cylinder 8 of the preionization unit 15, and the outer electrode 9 is a dielectric around the inner electrode 7 of the preionization unit 15. It may be attached so as to come into contact with the outer surface of the body cylinder 8.

In this embodiment, since the current-carrying member 25 and the outer electrode 9 are integrated, the preliminary ionization section 15 can be brought closer to the main discharge space than in the first embodiment, and reaches the main discharge space. The intensity of the ultraviolet rays 16 becomes stronger and the preliminary ionization becomes stronger, so that the laser characteristics can be improved.

By adopting the configuration of the first or second embodiment, in the gas laser device manufactured by the present inventor, the inductance of the discharge circuit which is 10 nH in the conventional case can be set to 6 nH. did it.

Although the gas laser device for emitting ultraviolet rays according to the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments and various modifications can be made.

[0044]

As is apparent from the above description, in the gas laser device for emitting ultraviolet rays according to the present invention, the connection point between the current-carrying member 25 and the conductive base 26 is located between the main electrode 4 and the preionization section 15. Since it is arranged so that the path from the main electrode 4 in the discharge circuit loop to the current introducing member 24 via the conductive base 26 and the current-carrying member 25 can be shortened, the cross-sectional area of the discharge circuit loop can be reduced. Can be made smaller.

By providing the opening 27 in the current-carrying member 25, the ultraviolet rays 16 for preionization can reach the main discharge space without being blocked by the current-carrying member 25, and the circulating laser gas flow flowing in the main discharge space can be achieved. 2 does not hinder the main discharge space from reaching.

In particular, if the current-carrying member 25 is formed as an integrated structure in which one metal plate is provided with the opening 27 removed, the thickness in the direction parallel to the direction of the laser gas flow 2 can be reduced, so that the main discharge is performed. The preliminary ionization part 15 can be brought closer to the space, the intensity of the ultraviolet rays 16 reaching the main discharge space is increased, and the preliminary ionization is increased, so that the laser characteristics can be improved.

Further, if the energizing member 25 and the outer electrode 9 are integrated, the preliminary ionization part 15 can be brought closer to the main discharge space, and the intensity of the ultraviolet rays 16 reaching the main discharge space is increased, and the preliminary ionization is performed. It becomes stronger and the laser characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a gas laser device according to a first embodiment of the present invention, which is perpendicular to a laser oscillation direction.

FIG. 2 is a side view of a main part of the gas laser device of FIG.

FIG. 3 is a sectional view of a main part of a gas laser device according to a second embodiment of the present invention, the cross section being perpendicular to the laser oscillation direction.

4 is a side view of a main part of the gas laser device of FIG.

FIG. 5 is a diagram showing a configuration example of an excitation circuit of a gas laser device.

FIG. 6 is a cross-sectional view of a main part of a conventional gas laser device, which is perpendicular to the laser oscillation direction.

[Explanation of symbols]

SW ... solid state switch HV ... high-voltage power supply C _1, C ₂ ... capacitors L _m ... nonlinear inductance (magnetic switch) C ₃ ... peaking capacitor C _11, C ₁₂ ... capacitor L ₀ ... inductance 1 ... laser chamber 2 ... laser gas stream 3, 4 ... Main discharge electrode 7 ... Inner electrode 8 ... Dielectric cylinder 9 ... Outer electrode 10 ... High voltage power supply 15 ... Corona preionization part 16 ... UV ray 21 ... Insulation base 23 ... Current introducing member 24 ... Current introducing member 25 ... Conducting member 26 ... Conductive base 27 ... Opening

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-10-135537 (JP, A) JP-A-10-125978 (JP, A) JP-A-10-335728 (JP, A) JP-A-9- 92917 (JP, A) JP 3-257980 (JP, A) JP 5-343782 (JP, A) JP 61-90485 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 3/097

Claims (2)

(57) [Claims] 1. A laser chamber having a laser gas enclosed therein and having a circulation means for circulating the laser gas therein, a pair of main discharge electrodes arranged at a predetermined distance in the laser chamber, and a pair of main discharges. The discharge circuit includes a peaking capacitor connected in parallel to the electrodes, and a preionization unit in which a first electrode and a second electrode are arranged to face each other via a dielectric, and the preionization unit is one main unit. In a gas laser device that emits ultraviolet rays and is arranged in close proximity to both sides of the discharge electrode, the one main discharge electrode is a ground side main discharge electrode, and the one main discharge electrode and the peaking capacitor. Are connected by a current-carrying member that passes between the one main discharge electrode and the preliminary ionization means, and the preliminary ionization means is covered with a second dielectric material. Is composed of a pole, a first electrode in contact with the dielectric material surrounding the second electrode, wherein the second electrode a high voltage is applied, the energization member and the first electrode are integrated A gas laser device that emits ultraviolet rays characterized by the above. 2. The current-carrying member is composed of a conductive plate having an opening, through which the laser gas passing through the main discharge space between the main discharge electrodes passes, and ultraviolet rays from the preionization means are passed. The gas laser device for emitting ultraviolet light according to claim 1, wherein the gas laser device is arranged so as to reach the main discharge space.